Kevin Hart is getting ready to welcome his son Kenzo any day now ... though preferably not this weekend!

ET spoke with the 38-year-old comedian on Saturday to talk about his exclusive underwear collection with Tommy John, where he also talked about running the New York City marathon on Sunday. Hart says his wife, Eniko Parrish, is a week and a half away from giving birth, and jokes that if their baby comes early, it might spoil his epic weekend plans.

"She’s about to drop," Hart says of Parrish. "My wife sneezes wrong, she’s gonna have that baby right now -- right now. She sneezes, that baby’s coming out. So, I just keep telling her, 'Hold it.' That’s what I keep telling her. 'Hold it!'"

"She’s trying to dance the baby out," he adds. "I told her to sit down. It can’t come out yet. I got two more things to do then that baby can come out. Don’t have this baby while I’m at this event, or I’m running this marathon. Don’t you do that. Because then I gotta stop everything and get back to the baby."

On a more serious note, Hart ccouldn't be more excited for his baby boy's arrival.

"You know, to have another addition to the family, especially a boy, the last name Hart lives on," he says. "It’s an amazing thing -- my third child. And it’s a time when you gotta look and be thankful for the blessings that you have, and more importantly, at the smiles I now get to see on a daily basis, you know. Both of my kids are excited, she’s excited. That’s the best thing for me. That’s the biggest gift that I could ask for. Nothing else comes close so, you know, we’re praying for a healthy delivery, healthy baby and I think smooth sailing from there on forth."

Hart did end up running the NYC marathon on Sunday, despite the rain. Hart told ET that his only wish was to not get a cramp.

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"I don’t want any bad memes out there," he explains. "You get a cramp and they get that picture that’s gonna last forever, so, I’m trying to keep my face as strong as possible throughout this marathon. No bad memes. That’s my motto. ... No limps across the finish line. That’s what I’m trying to do. You can assume that after the race you’ll see me in Tommy John loungewear and underwear on this plane back. I won’t take them off for a while. You won’t see me any athletic wear for a while after this run."

"The time to beat is, in a perfect world, under four hours," he adds about his goals. "In a world of reality, not knowing what I’m going to feel about mile twenty, seven and a half hours. ... Let’s just call it a 24-hour day."

On Sunday, Hart shared a sweet photo of his wife cheering him on the morning of the big day.

"Woke up to this amazingness this morning!!!!!" Hart wrote. "26.2 people....Operation destroy this New York Marathon is officially in session. I worked hard for this moment. No turning back now....Love you honey.... #HustleHart #RunWithHart #Harts #NYCmarathon."

Later, he showed off his medal after impressively completing the marathon. Hart said he did cramp up at around mile 20, but persisted nonetheless. The fit actor says he now wants to run four more marathons in the future.